FP<->int conversions remain.

Updates #16010.

Change-Id: I38d7a4923e34d0a489935fffc4c96c020cafdba2
Reviewed-on: https://go-review.googlesource.com/25589
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>